From 7e2dbedb22d6f89c1f91af57ee2d39403ec5aebc Mon Sep 17 00:00:00 2001
From: Tex Riddell <texr@microsoft.com>
Date: Tue, 4 Nov 2025 14:49:47 -0800
Subject: [PATCH] Fix linking of SV_PrimitiveID for Geometry Shader entry

This fixes a linking bug where the `SemanticKind` of a `SV_PrimitiveID`
input in a Geometry Shader gets erroneously replaced with
`SemanticKind::Invalid`.

When copying the input signature from the library module to the final
module during linking, new signature elements are constructed and
initialized using `DxilSignatureElement::Initialize` (there is not direct
copy constructor).  Initialize doesn't have an argument for the original
SemanticKind, normally constructing it based on the name and the
`SigPoint`.

However, the `SigPoint` for this element should be `GSIn` rather than
`GSVIn`, which is the default for all items in this signature. This causes
it to set the `SemanticKind` to `Invalid`.  There is code to correct for
this in `DxilSignatureElement::SetKind` used when initializing an element
from metadata, but that wasn't called in this signature copying code path.

This change updates `DxilSignatureElement::Initialize` to call `SetKind`
using the semantic looked up only by name.  `SetKind` will correct the
`SigPoint` if necessary and set the semantic by looking it up by
`SemanticKind` and `SigPoint`. This change also moves system value name
canonicalization to `SetKind`.
---
 lib/DXIL/DxilSignatureElement.cpp             |  8 ++++----
 tools/clang/test/DXC/link-gs-primitiveid.hlsl | 20 +++++++++++++++++++
 2 files changed, 24 insertions(+), 4 deletions(-)
 create mode 100644 tools/clang/test/DXC/link-gs-primitiveid.hlsl

diff --git a/lib/DXIL/DxilSignatureElement.cpp b/lib/DXIL/DxilSignatureElement.cpp
index bf8ee0abe0..c527c76932 100644
--- a/lib/DXIL/DxilSignatureElement.cpp
+++ b/lib/DXIL/DxilSignatureElement.cpp
@@ -50,10 +50,7 @@ void DxilSignatureElement::Initialize(llvm::StringRef Name,
   if (!IndexVector.empty())
     m_SemanticStartIndex = IndexVector[0];
   // Find semantic in the table.
-  m_pSemantic = Semantic::GetByName(m_SemanticName, m_sigPointKind);
-  // Replace semantic name with canonical name if it's a system value.
-  if (!m_pSemantic->IsInvalid() && !m_pSemantic->IsArbitrary())
-    m_SemanticName = m_pSemantic->GetName();
+  SetKind(Semantic::GetByName(m_SemanticName)->GetKind());
   SetCompType(ElementType);
   m_InterpMode = InterpMode;
   m_SemanticIndex = IndexVector;
@@ -136,6 +133,9 @@ void DxilSignatureElement::SetKind(Semantic::Kind kind) {
   // recover the original SigPointKind if necessary (for Shadow element).
   m_sigPointKind = SigPoint::RecoverKind(kind, m_sigPointKind);
   m_pSemantic = Semantic::Get(kind, m_sigPointKind);
+  // Replace semantic name with canonical name if it's a system value.
+  if (!m_pSemantic->IsInvalid() && !m_pSemantic->IsArbitrary())
+    m_SemanticName = m_pSemantic->GetName();
 }
 
 Semantic::Kind DxilSignatureElement::GetKind() const {
diff --git a/tools/clang/test/DXC/link-gs-primitiveid.hlsl b/tools/clang/test/DXC/link-gs-primitiveid.hlsl
new file mode 100644
index 0000000000..8335e57069
--- /dev/null
+++ b/tools/clang/test/DXC/link-gs-primitiveid.hlsl
@@ -0,0 +1,20 @@
+// RUN: %dxc -T lib_6_3 %s -Fo %t.dxl
+// RUN: %dxl %t.dxl -T gs_6_3 -E GS | FileCheck %s
+
+// Make sure link succeeds and produces correct system value for SV_PrimitiveID
+// i8 10 = DXIL::SemanticKind::PrimitiveID
+// CHECK: !{i32 1, !"SV_PrimitiveID", i8 5, i8 10, !{{[0-9]+}}, i8 0, i32 1, i8 1, i32 -1, i8 -1, null}
+
+struct GSINOUT {
+    uint id : ID;
+};
+
+[maxvertexcount(3)]
+[shader("geometry")]
+void GS(point GSINOUT input[1],
+        uint j : SV_PrimitiveID,
+        inout PointStream<GSINOUT> outStream) {
+    GSINOUT output = input[0];
+    output.id += j;
+    outStream.Append(output);
+}